1. Field of the Invention
The invention relates in general to an apparatus for changing optical disks, and more particularly to an apparatus for changing optical disk with incorporated elastic devices.
2. Description of the Related Art
Nowadays, as technology develops and changes with each passing day, and pictures, music, movies and computer software are applied more and more widely, optical disks with the advantages of large capacity, small volume, and secure data storage have become the predominant software loading tool. As a result, an optical disk drive, capable of reading optical disks and designed to simultaneously hold a number of disks in an optical disk drive, has become an essential PC peripheral. By means of the optical disk changer, a particular optical disk can be easily selected and read by the pick-up head of the optical disk drive.
FIG. 1A illustrates a top view of a conventional optical disk changer, and FIG. 1B shows a partially enlarged lateral view of the optical disk changer shown in FIG. 1A. As shown in FIG. 1A and FIG. 1B, an optical disk changer 100, mounted on a bottom plate 160 of an optical disk drive, includes at least driving shafts 102a, 102b, and 102c for clamping disk trays 104a, 104b, 104c, 104d, and 104e. These trays 104a-104e can be raised and lowered to position at different heights by rotating the driving shafts 102a, 102b, and 102c synchronously. The trays 104a, 104b, 104c, 104d, and 104e are provided for respectively holding optical disks 106a, 106b, 106c, 106d, and 106e (only the tray 104a and the disk 106a are shown in FIG. 1A), each of which has a round hole 150 at its center.
In FIG. 1A, there are projecting portions 108a, 108b, and 108c on the outer edge of the tray 104a, which have corresponding inserting holes 110a, 110b, and 110c and engaging projections 112a, 112b, and 112c respectively projecting from inner walls of the inserting holes 110a, 110b, and 110c of the tray 104a. The trays 104b˜104e are designed in the same way as the tray 104a. 
The driving shafts 102a, 102b, and 102c, respectively inserted into the inserting holes 110a, 110b, and 110c of the tray 104a (as well as those of the trays 104b-104e), are vertically mounted on the bottom plate 160, and are capable of rotating synchronously around their vertical axes. The driving shafts 102a, 102b, and 102c have threads 114 provided for engaging with the engaging projections 112a, 112b, and 112c of the tray 104a(as well as those of the trays 104b-104e). Each of the driving shafts 102a, 102b, and 102c can be divided into an upper thread region 116a, a middle thread region 116b, and a lower thread region 116c. The upper thread region 116a has the same pitch for threads 114 as the lower thread region 116c, and has a smaller one than the middle thread region 116b. 
As the driving shafts 102a, 102b, and 102c rotate synchronously around their vertical axes, the trays 104a-104e can be raised and lowered by the driving shafts 102a, 102b, and 102c, thereby allowing the disks 106a-106e to be positioned at different heights. In FIG. 1B, the tray 104a is engaged with the thread 114 in the upper thread region 116a so as to position the disk 106a in the range of the upper thread portions 116a. The trays 104c, 104d, and 104e are engaged with three adjacent threads 114 in the lower thread region 116c so as to position the disks 106c, 106d, and 106e in the range of the lower thread portions 116c. The tray 104b is engaged with the thread 114 in the middle thread region 116b so as to position the disk 106b in the range of the middle thread portions 116b. Since the pitch for threads 114 in the middle thread region 116b is larger than that in the upper and lower thread portions 116a and 116c, the tray 104b is farther apart from other trays 104a, 104c, 104d, and 104e. The disk 106b held at the tray 104b in the range of middle thread regions 116b can be carried to a disk loading in/out position to be loaded out and read by the optical disk drive, or the empty tray 104b can hold the optical disk loaded in by the optical disk drive.
As the number of the trays for holding disks is increased, the number of the threads 114 in the upper and lower thread regions 116a and 116c must also be increased, and the driving shafts 102a, 102b, and 102c must be elongated. As a result, the Optical disk drive equipped with the optical disk changer 100 will be thickened, departing from the preferential tendency of the optical disk drive to a thin and small design. Moreover, owing to the incline of the thread 114, the tray or the disk held at the middle thread region 116b cannot be precisely carried to the disk loading in/out position, thereby reducing the accuracy of positioning of optical disks.